--- title: "Caustics Tab" canonical: "https://documentation.chaos.com/space/VRAYHOUDINI/113279136/Caustics%20Tab" format: markdown --- This page provides information on the Caustics tab of the V-Ray Renderer. ## **Overview** --- ## **Parameters** --- > ✅ Tips when working with progressive caustics: > ✅ > ✅ **Required:** > ✅ > ✅ - **Affect Shadows** should be **off** in refractive materials if they are to generate caustics. > ✅ - The **Affect Channels** option should be set to **Affect all Channels** in refractive materials to ensure the **Caustics** **render element** contains also the ones fallen **behind refraction**. > ✅ Not doing so leaves photons fallen behind refractive surfaces inside the Refraction RE, but not inside the Caustics one. > ✅ - If present, the** VRaySun's photon emit radius** should be set to a value large enough to encompass the relevant parts in the scene. > ✅ > ✅ **Optional:** > ✅ > ✅ - It is **strongly recommended to set time limit** when rendering with Progressive Caustics, rather than relying on Noise Threshold value only. > ✅ - **Lower the Min. Shading Rate.** > ✅ Photons are cast for each camera ray, not for the secondary ones. The more camera rays are cast, the more photon passes are achieved. > ✅ A value of 3 is fine if rendering with the rest of the scene, but a value of 1 could be used if rendering specific caustic passes (for example, a caustics pass scene prepared with the purpose of maximizing caustics' calculation speeds). > ✅ > ✅ - **Set a higher min AA subdivs value.** > ✅ A higher min AA subdivs value (16, 24, even higher.) means there will be a longer phase of fixed sampling with no adaptation to the photon casting, so the screen coverage of samples will remain more consistent, allowing for quicker filling of, for example, big flat areas or long thin lines. > ✅ The later phase of rendering, with adaptation, will then just bring noise down to ensure Noise Threshold is respected. > ✅ > ✅ **Managing Expectations:** > ✅ > ✅ - **The progressive caustic solver is fire and forget.** > ✅ This means that it can be turned on in any scene, and *expected to trace photons on any specular or refractive surface*. > ✅ It doesn't, however, mean that doing so will result in an image converged to perfection within a short time. > ✅ The approach, novel as it is, is still photon-map based, and judgement should be used to ensure quick, noise and frustration-free results. > ✅ > ✅ - **It renders with the beauty.** > ✅ The solver does indeed render happily alongside a beauty pass, storing caustics in the appropriate Render Element (see requirements tips above!), but that may not be the best solution as far as performance is concerned. > ✅ It's suggested to consider preparing a dedicated caustic rendering pass if the photon tracing is particularly extensive, and/or if sequences are to be rendered. > ✅ That way, it will be possible to optimize the caustics calculation separately from the requirements of the beauty pass. > Macro (anchor) --- ### **Example: The Search Distance Parameter (Progressive)** For this example, the light used in the scene is V-Ray Sun. The Caustics Mode is set to **Progressive**. The V-Ray Sun has its Photon emission properties adjusted as so: **Caustics Subdivs** are set to 1500; the **Caustics Multiplier** is set to 2 and the **Photon Radius** is set to 30 cm. > Macro (anchor) > Macro (rw-ui-expands-macro) > > > Macro (rw-expand) > > > ### **Example: The Search Distance Parameter (Photon Map)** > > > For this image, the light's **Caustics Multiplier** parameter (||Light|| > Advanced properties rollout > Caustics Multiplier) is set to 80 and the rest of the parameters are at their default values. As seen from the images, the larger **Search Distance** produces blurrier caustics. > > > ![PhotonMap_SearchDist_1.5.png](media://ec3192ec-f959-42eb-bdd4-80771e6b2b7f) > > ![PhotonMap_searchDistance_2.5.png](media://a05e3aa3-fa0d-4836-a510-1189188a3345) > > ![PhotonMap_SearchDist_5.png](media://d995b722-3286-47d8-b9f1-9b92dbaa342f) > Macro (anchor) > Macro (rw-ui-expands-macro) > > > Macro (rw-expand) > > > ### **Example: The Max Photons Parameter** > > > In this example the light's **Caustics Multiplier** parameter (||Light|| > Advanced properties rollout > Caustics Multiplier) is set to 80 and the rest of the parameters are at their default values. VRaySun is used in this scene. As can be seen, the larger value of the** Max photons** parameter causes the caustics to appear much smoother. > > > ![MaxPhoton_example_10.png](media://b3b50925-22cb-40cf-8cfd-c46b90d4e439) > > ![MaxPhoton_example_60.png](media://ea1ddb69-aa15-47c8-9846-edf493ca6056) > > ![MaxPhoton_example_100.png](media://53f78dd9-f174-4751-b2d2-510853e7e8e9) > > ![MaxPhoton_example_200.png](media://38c7b575-788d-4e38-b66c-e01af9972ee3) > > ![MaxPhoton_example_300.png](media://2d23e2c7-9765-4184-9cab-ba66ee9e81f2) > Macro (anchor) > Macro (rw-ui-expands-macro) > > > Macro (rw-expand) > > > ### **Example: VRaySun Photon Radius** > > > This example shows how a light's photon radius affects the caustics effect. Here we use a VRaySun to light the scene. The **Caustics Multiplier** parameter in VRaySun's Advanced parameters rollout is set to 80 and the rest of the parameters are at their default values. > > > ![Caustics_SearchDist5_LightCausticsMult80_PhotonEmitRad5.jpg](media://34ae3176-dc42-409b-ad74-4e6798b92952) > > ![Caustics_SearchDist5_LightCausticsMult80_PhotonEmitRad10.jpg](media://c27baa32-92b1-488d-871b-71606dc3d918) > > ![Caustics_SearchDist5_LightCausticsMult80_PhotonEmitRad20.jpg](media://602af07f-0889-46a0-a5b1-e1d4b2f6a9e5) > > ![Caustics_SearchDist5_LightCausticsMult80_PhotonEmitRad40.jpg](media://c03dcef5-d412-4c6e-8f64-36e35372a7b5) > > ![Caustics_MaxPhotons60_LightCausticsMult80_ALLDEFAULTS.jpg](media://6f77ed30-7394-4c88-8e12-695e69c6fb3f) ## **Progressive Caustics Advantages** --- - They require nearly no setup. - Each cast photon is more useful than those in traditional Photon Mapping. - The number of photons castable is only limited by time, not memory. - They can resolve tiny caustic details, compared to the scene size. - They can resolve caustic details also when a camera is very zoomed in on them. - Statistics about the photon tracing can be found in the VFB2 stats panel. ## **Progressive Caustics Limitations** --- - They require the progressive image sampler. - The image sampler often requires Min. subdivs values much higher than 1. - It's non-deterministic, meaning that there could be somewhat unpredictable render times, and also tiny differences in the visual results when rendering the same frame twice. - Currently doesn't work with distributed rendering. - Currently not supported by the GPU engine. - Depending on the scene, the performance might not scale linearly with the number of threads/cores, resulting in inefficient CPU utilization. ## **Notes** --- - Caustics also depend on the individual light settings. - For accurate caustic calculations, *disable *the [V-Ray Material's](https://docs-chaos.atlassian.net/wiki/spaces/VRAYHOUDINI/pages/113279382) **Affect Shadows **parameter when using caustics. Simultaneous usage of both **Caustics** and** Affects Shadows** can be used for artistic purposes but will not produce a physically correct result. - V-Ray GPU supports Caustics rendering within the following limitations: - Texture lights are not supported. - Rendering with V-Ray GPU with RTX is not supported. - V-Ray Blend material is not supported. - Dispersion is not supported. - The supported lights are: V-Ray Rectangle Light and V-Ray Sun Light.